In the art of making aluminum complex greases, two methods of preparation are commonly employed. In one of these methods, an aluminum alkoxide is dissolved in an oil stock and two mole equivalents of an acid or acid mixture is added thereto. During subsequent heating, reaction occurred releasing one mole of alcohol per mole of acid introduced. Thereafter to the resulting system water is added which reacts with the final remaining alkoxy group thereby releasing the third and final mole of alcohol and producing a hydroxyl group on the aluminum atom. The alcohol produced is removed by distillation and, since the water is typically added in excess, the excess water is likewise removed by distillation. A typical aluminum alkoxide employed in this method is aluminum isopropoxide; see, for example U.S. Pat. No. 3,345,291 issued to Chevron research corporation.
In the second technique, a cyclic aluminum isopropoxide (or other alkoxide) trimer is introduced into a mineral oil. To this mixture is added a carboxylic acid mixture which is approximately equal to two moles of acid per mole of aluminum. When this mixture is heated, reaction occurs which releases one mole of alcohol per mole of aluminum. See, for example, Rinse U.S. Pat. No. 3,054,816. Apparently, it is possible to reverse the order of addition so that the cyclic aluminum isopropoxide trimer is added after the acids are introduced into the petroleum oil; see, for example, column 4 of Bailey et al U.S. Pat. No. 3,776,846. The alcohol thus produced as a by-product is removed by distillation.
So far as is now known, no one has heretofore commercially employed oxyaluminum acylates in combination with organic acids to prepare greases of mineral oils in such a way as to avoid the problem of removing alcohol produced as a by-product in the grease manufacture and to avoid the addition and/or removal of water present in a system. In Rinse U.S. Pat. No. 3,054,816 (see column 3, lines 53-57), it is suggested that a cyclic aluminum oxide stearate trimer can be mixed with mineral oil and then reacted with benzoic acid at elevated temperature to produce a grease. This suggestion of Rinse, so far as is known, has never been commercially exploited. Moreover, the properties of the grease made by the Rinse procedure are not equivalent to the properties of greases made by using oxy aluminum acylates wherein the rate of the number of aromatic radicals to aliphatic radicals of the cyclic timer compound range from about 2:3 to 3:1.
In Harson British Pat. No. 825,878 cyclic organoaluminum timers and linear organoaluminum polymers are used in greases. Thus, mixed benzoate/stearate oxyaluminum acylate trimers are shown (see page 4, lines 100-110, Example 3, and Example 17 of Harson), as are greases made with cyclic trimers (see Examples 25 and 28. Harson used only low amounts of benzoic acids in his organoaluminum compounds (not more than 35 mole %) and he experienced difficulty in making smooth greases without lumping. In Example 28 thereof for example, when benzoic acid is present in the "external acids," certain other acids (such as branched chain and short chain acids or dimer acids or unsaturated acids or hydrogenated castor fatty acids must be present. Also, presolution of benzoic acid is needed to get a smooth grease. Harson never utilized oxyaluminum acylates wherein the ratio of number of aromatic radicals to aliphatic radicals of the cyclic timer compounds ranged from about 2:3 to 3:1.